Ventricular function will be measured in healthy volunteers and patients with heart disease as they pursue their activities of daily living. Information about ventricular function will be recorded with a lightweight nuclear probe device that will be worn by the patient. The nuclear data will be recorded in synchrony with two lead electrocardiographic information over an interval of 6-8 hours. Initially, measurements of ventricular function and electrocardiographic response made in the stress laboratory will be compared to those made while the patients pursue their routine activities to define both the incidence and duration of changes in ventricular function and EKG. Additional studies will evaluate the augmentation of ventricular function response due to post premature ventricular beats; the improvements in ambulatory ventricular function in patients undergoing valve replacement, evaluation of propranolol treatment in the setting of impaired left simultaneously in patients with right ventricular overload. These studies should define the role of continuous monitoring of ventricular function in comparison to studies performed in the stress laboratory in the management of patients with heart disease.